High frequency generator and modulator



Sept. 5, 1933. H D 1,925,534

HIGH FREQUENCY GENERATOR AED MODULATOR I 2. E. E

/7 /4 ll 4 4/ w E1, LOAD /5 /9 :1 Z I 20/ 1; 5 /2 f LOAD 3 INVENTOR Angus-i Hnnfl ATTORNEY Patented Sept. 5,- 1933 UNITED smrss HIGH FREQUENCY GENERATOR AND MODULATOR 7 August Hund, West Orange, N. J., assignor to Wired Radio, Inc.,-New York, N. Y., a corporation of Delaware Application September 1 7,- 1931 Serial No. 563,316

4 Claims. 1 ('01. 179- 171) v My invention pertains in general to radio signalling and specifically relates to a system for producing modulated high frequency currents.

One of the objects of my invention consists in 5 providing a circuit for producing modulated high frequency oscillations in which modulation currents are produced in the circuit before the generation of the high frequency oscillations.

Another object consists in providing a system for producing modulated high frequency oscillations from modulated relaxation oscillations of a lower frequency A further object comprises producing a system for developing a plurality of discrete high frequency oscillations from a single source of low frequency relaxation oscillations.

A still further object consists in providing meansfor developing a plurality of discrete high frequency oscillations under control of a common modulator. 1

I accomplish these and otherjdesirable objects in a novel high frequency generator and 'modulator having a microphone controlled relaxation circuit including a glow discharge tube for producing the recurrent energization of a plurality of circuits tuned to discrete high frequencies.

In the drawing which accompanies and forms apart of this specification and in which like reference characters designate corresponding parts throughout:

Fig. lis a diagrammatic representation of one embodiment of the high frequency generator of my invention showing a system, for producing modulated high frequency oscillations of a single high frequency;

Fig. 2 is a diagrammatic representation of a modification of the system of Fig. 1 in which means'are provided for producing a plurality of discrete high frequency oscillations.

Referring to the drawing in detail and particularly to Fig. 1, there is provided aglow discharge tube 1 which comprises an envelope enclosing a pair of electrodes 2 and 3. In the present embodiment of my invention this envelope is provided with an attenuated atmosphere of helium.

I have found that satisfactory results can be obtained for the production of oscillations by maintaining this atmosphere of helium at a pressure of substantially 12 mm of mercury. It will be understood that other suitable gases can be used in lieu of helium, and at other suitable pressures. The electrodes 2 and 3 are of a small area and disposed in a manner such as to reduce interelectrode capacitance to a minimum. The electrodes 2 and 3 are connected with an external circuit including a resistance 4, a source of direct current 5, and an inductance 6, all connected in series. The inductance 6 comprises the secondary winding of an audiofrequency transformer having a primary winding 7. The primary winding '7 is connected in series with a microphone 8 and source of current 9. The circuit l---8--9 is indicative of any source of modulation currents. v I

Connections from the electrodes 2 and 3 are further extended to include a circuit having a variable condenser 10 and an inductance 11.

The inductance 11 is electromagnetically coupled to an inductance 14 connected in series with a condenser 17 and a load 18. Thecircuit 141 7. 18 is resonant to a desired high frequency designated as the frequency f1. In this specification the term high frequency will be used as denoting inaudible frequencies used for carrier purposes in wired radio or space radio signalling The load 18 is indicative of any work circuit or device for the utilization of modulated high frequency oscillations produced according to my system. If the load 18 is an amplification circuit coupled with power lines for wired radio signalling, the condenser 17 is conveniently connected across the inductance 14 and the resonance voltage across this parallel circuit is applied to the amplifier.

v In accordance withmy invention, the source of current 5 appliesa potential difference to the electrodes 2 and 3 which is of'a magnitude sufficient to initiate a glow or ionization discharge. The voltage necessary to bring about this glow discharge will be called the ignition voltage. If the resistance 4 is of a proper value, the glow discharge which takes place across thev electrodes 2 and 3 will produce a potential drop across the resistance 4, whereby-the voltage across the electrodes 2 and 3 will become reduced. As soon; as the voltage across the electrodes 2 and 3 becomes smaller than the lower critical voltage, the glow discharge will be quenched. The foregoing functions will be repeated to produce continuous re- 0 oscillations are developed. It is of course well known that relaxation oscillations such as produced by the glow discharge tube 1 have a tendency toward unstability, are of poor wave shape, and are generally limited to the lower frequencies. It will be evident thenthat such relaxation oscil lations would normally be unsatisfactory for most purposes'as in signalling modulated high frequency energy.

However, in accordance with my invention the relaxation oscillations produced by the glow discharge tube 1 and associated circuit just described produce impulse energization of the circuit 10- 11. The circuit 10-11 has parameters of a value such that this impulse energization will set up oscillatory currents at frequencieswhichwiil he harmonics of the fundamental frequency f0 of the relaxation oscillations. The resonant circuit comprising the inductance 14 and capacitance 17 is tuned to a desired high frequency [1 which is a particular integral multiple of the fundamental relaxation frequency f0. This frequency f1 appears in the resonant circuit 10-11 and is se' lected by the circuit 14-1? for effecting the transfer of oscillations at the desired frequency f1 to the load 18. These oscillations transferred to the load 18 will be modulated under control of the microphone 8. An alternative form of the circuit of Fig. 1 consists in connecting a capacitance 23 (shown dotted) in parallel with the inductance 11 to form a closed circuit 11-23 for accentuating oscillations at the frequency h of circuit 14-17.

Fig. 2 represents a development of the circuit of Fig. l in accordance with my invention in which means are provided for developing plurality of discrete high frequency currents having common modulation. Referring to Fig. 2

; in detail, the circuit shown is substantially identical with the circuit of Fig. '1, except that the inductance 11 is connected in series with inductances 12 and 13 which are electromagnetically coupled to inductances 15 and 16 respectively. The inductance 15 is connected in series with a condenser 19 and load it), while the inductance 16 is connected in series with a condenser 21 and load 22. The loads ZOand 22 be considered as indicative of any suitable work circuits or de vices for the utilization of modulated high frequency currents and are similar to the load 18. The circuit 15-19 is resonant to a particular high frequency f2 while the circuit 16-21 is resonant to a different high frequency f3. The frequencies f2 and is, as well as the frequency ii are different harmonics of the fundamental frequency f0 of the relaxation oscillations produced by the glow discharge tube 1. These frequencies all appear in the circuit 10-11-12-13, due to the recurrent impulse energization of the relaxation oscillations. In experiments the circuits 14-17, 15-19, and 16-21 were tuned to 26, 39, and 52 kilocycles, respectively, whereby commonly modulated carrier currents of such frequencies were developed for simultaneous transmission purposes.

It will now be apparent that I have provided a novel high frequency generator and modulator in which modulated high frequency oscillations are developed from low frequency relaxation oscillations under control of an associated microphone. Although I have shown a preferred embodiment of my high frequency generator and 'modulator it will, of course, be understood that modifications can he made therein without departing from the intended scope of my invention. I do not therefore desire to limit myself to the foregoing except insofar as may be pointed out in the appended claims.

, What I claim as new and original and desire to secure by Letters Patent of the United States 1. In a high frequency generator and modulater, a relaxation system comprising, a glow discharge tube, a direct current circuit path including said glow discharge tube and having an eifectiveresistance-therein, an oscillatory circuit path also including said glow discharge tube and having inductance and c 'pacitance therein, said direct current circuit path having means therein for preventing oscillatory currents of a nature produced in said oscillatory circuit from passing therethrough, said oscillatory circuit being adapted to prevent the passage of direct current therethrough, said relaxation system as a whole operating to produce a wide band of oscillation frequencies including low frequencies and high frequencies, control -means for varying the current flow through said direct current circuit path whereby said low and high frequencies in said oscillatory circuit are accordingly'controlled; and means for selecting desired high frequency oscillations from said oscillation circuit to the exclusion of said lowfrequency oscillation circuit,

said high frequency oscillations being controlled in accordance with the controlling effect exerted upon said direct current circuit path of said low frequency system.

2. A high frequency generator and modulator in accordance with claim 1 in which said controlled means comprise a modulation circuit having a microphone connected therein.

3. A high frequency generator and modulator in accordance with claim 1 in which said last mentioned means comprise a plurality of resonant circuits each tuned to a different high frequency.

4. A high frequency generator and modulator in'accordance with claim 1 in'which said controlled means comprise a modulation circuit having a microphone connected therein, and said last mentioned means comprise a plurality of resonant circuits tuned to discrete high frequencies having harmonic relationship.

- AUGUST HUND.

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